The present invention relates to a position control apparatus for controlling the rotation position of an electric motor and more particularly to an electric motor position control apparatus for adjusting control parameters.
As a prior art regarding electric motor position control, an art (a first prior art) described in Japanese Patent Specification No. 2890529 is known. This first prior art will be described below.
FIG. 30 is a block diagram showing the configuration of a control system in an electrical motor position control apparatus in accordance with the first prior art. The control system in the electric motor position control apparatus shown in FIG. 30 is provided with not only a position feedback loop for the rotation position of an electric motor 501 but also a speed feedback loop for controlling the rotation speed of the electric motor 501 and a current feedback loop for controlling the current of the electric motor 501. In the current feedback loop, control is carry out so that an error between a value obtained by digital-to-analog converting the output value of a speed control section 507 and a motor current supplied to the electric motor 501 become zero. In the speed feedback loop, control is carry out so that the output value of a position control section 505 becomes equal to a motor speed calculated by a speed calculation section 506. Then, in the end, in the position feedback loop, control is carry out so that the error between a position detected by a position detector 502, such as a pulse encoder or a linear scale, and a position command value issued from a command issuing section 503 becomes zero.
The output from the position detector 502 is input to a position counter 504 and converted into the rotation position of the electric motor 501. The speed calculation section 506 calculates rotation speed from the output of the position detector 502. As shown in FIG. 30, the error between the rotation position and the position command value issued from the command issuing section 503 is input to the position control section 505, and the position control section 505 outputs a speed command value. The error between this speed command value and the rotation speed from the speed calculation section 506 is input to the speed control section 507, and the speed control section 507 outputs a command value for driving the electric motor 501. This command value is input to a power amplifier 509 via a D/A converter 508. The power amplifier 509 drives the electric motor 501 in accordance with the input from the D/A converter 508.
In FIG. 30, numeral 510 designates a parameter change judgment section having a function of changing the control parameters of the position control section 505 and the speed control section 507. In addition, thick line arrows in FIG. 30 indicate digital amount signals, thin line arrows indicate analog amount signals, and broken line arrows indicates indication signals.
The operation of the parameter change judgment section 510 shown in FIG. 30 will be described below.
First, the speed control section 507 carries out proportional control (P-control). A block diagram showing the entire control system at the time when the speed control section 507 carries out P-control is shown in FIG. 31. FIG. 31 is a block diagram in the case when the response frequency of the current feedback loop can have been set high to the extent that it can be made constant and when the speed feedback loop can be approximated by a linear expression. Furthermore, it is assumed that the gain of a controlled object in consideration of the gain of the current feedback loop, which is made constant, a motor torque constant, the total inertia of the electric motor and a load, the resolution of the position detector 502, etc. is 1/J.
The transfer function G2(S) of the entire control system shown in FIG. 31 is represented by the following equation (1)G2(S)=1/{1+(b1/b2)S+(1/b2)S2}  (1)wherein                b1=Kvp·KFB/J,        b2=Kpp·Kvp/J,        Kvp is the proportional gain of the speed control section 507,        Kpp is the proportional gain of the position control section 505, and        KFB is the feedback gain of the speed feedback loop.        
When the proportional gain Kvp of the speed control section 507 is fixed to a value capable of making the characteristic frequency of a processing apparatus serving as the controlled object negligible, and when the proportional gain Kpp of the position control section 505 is set so as to be higher than the proportional gain Kvp, the servo system gradually becomes vibratory. When it is assumed that the vibration frequency is fi, the vibration frequency fi has a relationship represented by the following equation (2) with respect to the proportional gain Kpp and the proportional gain Kvp.fi=(½π)·(Kpp·Kvp/J)1/2[Hz]  (2)
At this time, the vibration frequency fi is measured while the electric motor 501 is driven by a position command issued from the command issuing section 503. Then, on the basis of the equation (2), the gain of 1/J of the controlled object including the constants, such as the inertia of the electric motor 501 and the load, is obtained.
Then, the operation of the speed control section 507 is switched to integral-plus-proportional control (IP-control). When it is assumed that the proportional gain and the integral gain of the speed control section 507 is Kvp and KVI, respectively, and that the integral gain KVI of the speed control section 507 is nonzero (a value other than zero), a block diagram at this time is shown in FIG. 32. The transfer function G1(S) of the entire control system at this time is represented by the following equation (3).G1(S)=1/{1+(a2/a3)S+(a1/a3)S2+(1−/a3)S3}  (3)wherein                a1=Kvp·KFB/J,        a2=KVI·KFB/J, and        a3Kpp·KVI/J.        
In the control system in accordance with the first prior art configured as described above, while the relationship among the three gains, that is, the proportional gain Kvp and the integral gain KVI of the speed control section 507 and the proportional gain Kpp of the position control section 505, are maintained constant, the above-mentioned three gains are raised gradually until a resonance state occurs between the response frequency component of the electric motor 501 and the characteristic frequency of the processing apparatus serving as the controlled object. After the resonance state has occurred, the above-mentioned three gains are lowered gradually in reverse and the gains at the time when the resonance stops are set as optimum gains.
In addition, as another prior art relating to electric motor position control, an art (a second prior art) disclosed in the publication of Japanese Laid-open Patent Application No. Hei 10-56790 is available. An electric motor position control apparatus in accordance with the second prior art will be described below by using the drawings.
FIG. 33 is a block diagram showing the system configuration of the electric motor position control apparatus in accordance with the second prior art.
In FIG. 33, an electric motor 601 is driven by motor torque, and a load machine 602 is driven by the motor 601. The rotation position and the rotation speed of the electric motor 601 are detected by a rotation detector 603. A torque control circuit 604 matches the motor torque with a torque command signal. A position command signal generation circuit 605 generates a position command signal serving as a position command for the electric motor 601 and the load machine 602 and outputs the position command signal to a feedforward circuit 608. The feedforward circuit 608 receives the position command signal and outputs a feedforward signal, a response target position signal and a response target speed signal.
As shown in FIG. 33, the position control apparatus in accordance with the second prior art is provided with a speed compensation circuit 606, a position compensation circuit 607, a switch 609, a torque command signal generation circuit 610 for drive tests and an automatic adjustment circuit 611.
Next, the operation of the position control apparatus in accordance with the second prior art configured as described above will be described.
First, the switch 609 is switched to its contact (b), whereby the torque command signal generation circuit 610 for drive tests outputs a torque command signal, such as a pseudo-random signal, to the torque control circuit 604. The torque command signal generation circuit 610 for drive tests outputs the torque command signal to the torque control circuit 604 and carries out a drive test on the electric motor 601. The torque command signal and the rotation speed of the electric motor 601 obtained at this time are input to the automatic adjustment circuit 611.
The automatic adjustment circuit 611 calculates the parameters of its built-in high-order transfer function model by using the method of least squares, for example, thereby identifying a transfer function in the range from the torque command signal of the controlled object to the rotation speed of the electric motor in detail. The absolute value of the smallest complex zero point of the identified transfer function is selected as an estimated antiresonance frequency ωze. In addition, a total inertia Je is estimated from the gain characteristic in the low frequency range. Either a two-inertia system optimum gain Kopt calculated by using this estimated antiresonance frequency ωze and the estimated total inertia Je or a limit gain Kmax obtained by using the frequency characteristic, gain margin and phase margin of the transfer function, whichever smaller, is determined as the speed gain Kv of the speed compensation circuit 606. The position gain Kp and the position integral gain KpI of the position compensation circuit 607 are determined on the basis of the determined speed gain Kv by using predetermined calculation equations. In addition, the gain parameters of the feedforward circuit 608 are calculated and determined by using the estimated antiresonance frequency ωze and the estimated total inertia Je.
As described above, in the first prior art disclosed in Japanese Patent No. 2890529, while the relationship among a plurality of gains was maintained constant, the resonance state occurring between the electric motor and the controlled object was detected, and optimum control parameters were determined. In the case when the controlled object has a resonance frequency, the values of the control parameters are made larger by inserting a filter for suppressing the component of the resonance frequency, whereby responsivity can be raised; however, this kind of adjustment method was insufficient for the adjustment of the control parameters.
Furthermore, in the second prior art disclosed in the publication of Japanese Laid-open Patent Application No. Hei 10-56790, in order to set the control parameters so as to be stable for the controlled object having a resonance characteristic, it is necessary to measure the estimated value of the antiresonance frequency of the controlled object and the frequency resonance value of the controlled object. In order to obtain these values, operations, such as measurements conducted by supplying test signals, were necessary.